The invention relates to a method for processing information in a wireless local loop (WLL) terminal and to a WLL terminal. The invention can be applied in wireless local loop systems to realize services using character-based information.
WLL systems provide an economic way of expanding the public switched telephone network to new subscribers as the expansion can be realized without installing new cables for the new subscriber connections. Terminals in wireless local loop (WLL) networks comprise a telephone set or other subscriber equipment with the transceiver unit connected to it which are suitable to be connected to the public switched telephone network. The matching between the subscriber equipment and the transceiver unit is provided by a line adapter. Generally, the transceiver unit is connected via a radio path to a cellular service such as the GSM system. Often, a subscriber connection is used for transferring both speech and graphic information such as facsimiles, in which case the terminal comprises a telephone apparatus and a fax machine, for example. However, as regards the operation of such a WLL terminal, there are some restrictions to be considered, as will be shown later on.
Next, we will give a description of the prior art by first disclosing in greater detail a known WLL terminal and how it is connected to a WLL telecommunication system.
FIG. 1 shows a known arrangement for realizing a WLL terminal. A WLL terminal 100 is connected to a cellular system which includes base stations 151 for transferring information via the radio path to terminals by means of an antenna 150. The base stations are connected to base station controllers 152 which are further connected to an exchange 153. The exchange 153 is connected to a public switched telephone network PSTN. The exchange includes a home location register HLR which stores information about the subscribers in the system. In addition, digital cellular systems may include a short message service center SMSC 155 for conveying short messages. However, short messages cannot be communicated with prior art WLL terminals.
The terminal 100 comprises an antenna 104 for transmitting and receiving a radio-frequency signal. The received signal is amplified and demodulated into a baseband signal in a RF part 113, and the baseband signal is processed in the signal processing block 114 in the baseband part 110 (BB). Correspondingly, the baseband signal to be transmitted is processed according to the cellular system specifications in block 114 and modulated into a RF signal and amplified in the RF part 113 so as to be sent to the antenna 104.
Signal processing and the RF part are controlled by a processor 111 which has a memory unit 112 for storing programs and parameters. A regulator 115 produces operating voltages for the baseband part and the RF part.
A line adapter part 130 (LA) includes an audio part 134 which matches the audio signal of the baseband part 110 to the audio signals of the telephone apparatus 101 and the fax machine 102. A DTMF indicator 133 detects the dialling signals transmitted via the audio line and conveys them to the processor 131 of the line adapter part. A HOOK indicator 135 detects the status of the receiver hook of the telephone apparatus and conveys the status information to the processor 131 and to a tone generator 136. The tone generator 136 generates the tones for the telephone apparatus 101 and fax machine 102 according to the connection status information sent by the cellular system. A ring generator 137 produces a high-voltage ringing signal (say, 45 V AC) for the ringing function of the telephone apparatus. The line voltage/loop current (say, 40 V DC) is produced by a DC generator 138 so that it corresponds to the specifications of the telephone apparatus 101 and the fax machine 102. The processor 131 controls the line adapter blocks and is connected to the processor 111 of the mobile part 110 via a serial interface, for example. The memory 132 of the processor 131 is used for storing the processor software, connection status information and the parameters related to the line adapter functions, among other things. The WLL terminal further comprises a battery unit 103 and regulators 115 and 139 to produce the operating voltages for the equipment. The WLL terminal blocks 103, 110, 113 and 130 usually constitute an integrated equipment block 120.
The prior art solution described above is disclosed in more detail in patent document 1! U.S. Pat. No. 5,117,450 (WO 9014729). Other WLL systems according to the prior art are described in patent documents 2! U.S. Pat. No. 4,658,096, 3! U.S. Pat. No. 4,737,975, 4! U.S. Pat. No. 4,775,997 and 5! U.S. Pat. No. 4,922,517, for example.
In the conventional WLL systems, the user has access only to the services of the public switched telephone network PSTN. WLL systems that are based on e.g. the GSM/DCS system often include other services, too, such as the short message service, information on received calls, etc., and these services usually involve displaying of information which is processed in the system in the form of characters. Processing and displaying of such information is not possible in the WLL systems of the prior art, so the user of a WLL terminal can have no access to these services.